Investigation of Nitrate pollution in the Soil, Water and Plants in Some Agricultural Fields in Baraan (Esfahan)

There is concern about the harmful effect on human and animal health of excessive nitrate concentrations in edible plants. Numerous studies have been made throughout the world on nitrate accumulation, especially in vegetable plants. Therefore, studies are necessary to assess the local nitrate content of vegetable crops in major production areas. The soil, water and vegetable nitrate level were studied in Northern Baraan (20 Km East of Esfahan in the old alluvial plain of the Zayandeh-roud River in Central Iran) for two years. The vegetables selected consisted of: leafy and stem vegetables including leek, dill, fenugreek (Trigonell), spinach, mint, sparsely and chinese parsley; root vegetables including onion, potato and tomato; and fruit vegetables including the commonly grown of cantaloupe melons and cucumber. For each plant, three fields with similar cultural management were selected. In each field, at the beginning and end of the growing season, the top 0-30 cm of soil and irrigation well-water were sampled in three replicates. Also, edible plant parts were sampled in three replicates, in the morning and afternoon. Soil nitrate concentrations in most of the vegetable fields were higher than permissible levels, showing excessive nitrogen fertilizer application. The results showed that nitrate concentration over 75% and 79% of the soil study area was higher than the permissible level of 20 mg/kg in the first and second years, respectively. The nitrate concentration of most of the irrigation well-water was higher than the permissible range of 10 mg/l, which is the threshold limit for direct human and animal consumption and for land irrigation. The highest nitrate content in stem and leafy vegetables was found in sparsely (mean of 2121 mg/kg), and onion (mean of 238 mg/kg). The lowest nitrate concentration in leafy vegetables was found in spinach (mean of 20.8 mg/kg) and cucumber (mean of 89 mg/kg). The ranges of nitrate concentration in stem and leafy vegetables were 4 to 6,297 mg/kg and in root vegetables were 17.3 to 872.4 mg/kg fresh weight. The nitrate content of all stem and leafy vegetables except spinach, bulb and of fruit vegetables, except cucumber, were higher than permissible limits. In leafy, bulbous and fruit vegetables nitrate concentrations were higher than the permissible concentration level of 67-mg/kg fresh weight. The effect of the time of plant sampling in the morning and afternoon on nitrate content was significant. Timing of sampling shows that the nitrate level in stem and leafy vegetables were significantly lower in the afternoon than in the morning and nitrate content decreased during the day.